After 2 years with a Stage 1 H-D air cleaner and slip-ons on my 2010 RK, I went with the Fuel Moto 2>1>2 pipes (I did not get the ceramic coating) and their 4 in. slip-ons, but at the same time, I also did Andrews 48 cams and a ThunderMax, so not sure how much of my new boost is due to the pipes. About all I can say is that FM was great to work with, the price was right, and they look good. I also liked being able to use my like-new heat shields and not having to pay for new ones.
I think I understand that these pipes are very similar to V&H Power Duals - will probably hear negative feedback on that, but that's what I understand.
BTW...FM had a hellofa wait to get the ceramic coating for the pipes and understand the gains for a non-racing application was marginal.